1. Field of the Invention
The present invention relates generally to imaging systems for obtaining images of a specimen. More particularly, the invention concerns an imaging system which includes a camera and a novel filter grid that is controllably movable relative to the camera in a manner to strategically move a selected emission filter grid, comprising a plurality of emission filters, into position between the camera and the specimen.
2. Discussion of the Prior Art
Imaging systems of many kinds are widely used in the prior art to obtain images of various types of objects. Typically the imaging system includes a camera and oftentimes one or more special filters that are positioned between the camera lens and the object to filter the light reaching the camera.
The apparatus of the present invention is particularly useful in the field of fluorescence imaging, but is not limited to this application. Fluorescence imaging is typically performed by illuminating a specimen in a manner to excite fluorescing molecules in the specimen, and then, using a suitable camera, capturing an image of the specimen as it fluoresces.
As a general rule, intensified or cooled charge-coupled device (CCD) cameras are used to detect the fluorescence of low intensity light radiating from the sample. The image capture, of course, requires that the specimen be illuminated with a suitable illumination source, while the minute amounts of fluoresced energy from the “excited” sample are detected using the CCD camera. In carrying out the imaging process, the CCD camera is typically fixed at a single location over a specimen supporting platform and the operator places a specimen in a predetermined position on the specimen supporting platform within the field of view of the overhead camera.
In obtaining the desired image of the specimen, it is generally necessary to position an appropriate emission filter between the specimen and the camera to filter out the excitation light rays and leave substantially only the fluorescent rays emanating from the sample. In the prior art, an emission filter wheel has been used to accomplish the appropriate filtering out of the excitation light rays. This filter wheel is typically housed within the imaging chamber within which the specimen resides and is rotatable in a manner to bring a selected one of the circular shaped emission filters carried by the filter wheel into a position between the specimen and the lens of the camera wheel. Such a construction is provided in an imaging station sold by the Kodak Digital Science Company using the model number 440CF. The filter wheel of this latter system contains filters for different detection methods and includes five standard 58 mm filters positioned in circumferentially spaced apart locations.
As will be discussed in greater detail hereinafter, the apparatus of the present invention constitutes a substantial improvement over the prior art filter wheels and includes a novel X-Y array, or grid, within which nine generally rectangular shaped filters are mounted. In the preferred embodiment of the invention, the grid can be quickly and precisely moved by means of electric motors along both the X- and Y-axes of the grid system in a manner to bring a desired one of the emission filters into position between the specimen and the camera lens.
Prior art imaging systems include, by way of example, the system disclosed in U.S. Pat. No. 5,175,437 issued to Waluszko. More particularly, this patent describes an apparatus for irradiating an object such as a specimen of material with ultraviolet radiation at selected long, short or mid-wave length.
U.S. Pat. No. 5,736,744 issued to Johannsen, et al. discloses a wavelength-shifting filter having two sheets of material adjacent and parallel with a spacer there between and with the sheets held in a frame. A phosphor coating is located on the inner side of one of the sheets. A transilluminator is associated with the filter and provides radiation in the UV wavelength. One sheet of the filter transmits the UV wavelength. The other sheet transmits at least a portion of the wavelength that the phosphor coating generates when subjected to the UV radiation of the transilluminator.
In a somewhat similar vein, U.S. Pat. No. 3,936,186 issued to Boland et al., discloses an apparatus for exposing diazo printing plates and the like of the character that are used in the graphic arts field. In like manner, U.S. Pat. No. 5,288,647 issued to Zimlich, Jr. et al., relates to a method by which polynucleotide specimens can be irradiated particularly for the purpose of fixing them to a substrate.
U.S. Pat. No. 5,951,838 issued to Heffelfinger et al., concerns a method and apparatus for achieving uniform illumination of an electrophoresis apparatus. In the Heffelfinger et al., method, uniform illumination is achieved by scanning the light source across the sample gel in a direction perpendicular to the axis of the source. The light source is comprised of one or more light bulbs placed in a light tray. Variations in light intensity near the source end portions is minimized using a variety of techniques including extended light bulbs, filters, reflectors, and diffusers, or supplemental sources.